docs: def download_sst(path, url):
      """"
      Download from `url` the zip file corresponding to the
      Stanford Sentiment Treebank and expand the resulting
      files into the directory `path` (Note: if the files are
      already present, the download is not actually run).
  
      Arguments
      ---------
          path : str, directory to save the train, test, and dev files.
          url : str, location of zip file on the web
  
      Returns:
      --------
  
          dict<str, str>: file path for the keys train, test, dev.
  
      """
      local_files = {
          "train": join(path, "train.txt"),
          "test": join(path, "test.txt"),
          "dev": join(path, "dev.txt")
      }
      makedirs(path, exist_ok=True)
      if all(exists(fname) and stat(fname).st_size > 100 for fname in local_files.values()):
          return local_files
  
      zip_local = join(path, 'trainDevTestTrees_PTB.zip')
      delete_paths([zip_local, join(path, "trees")] + list(local_files.values()))
      utils.urlretrieve(url, zip_local)
      ZipFile(zip_local).extractall(path)
      for fname in local_files.values():
          move(join(path, 'trees', fname.split('/')[-1]), fname)
      delete_paths([zip_local, join(path, 'trainDevTestTrees_PTB', 'trees'), join(path, 'trainDevTestTrees_PTB')])
      return local_files